Split-cycle air hybrid engine

ABSTRACT

A split-cycle air hybrid engine operatively connects an air reservoir to a split cycle engine. A power piston is received within a power cylinder and operatively connected to a crankshaft such that the power piston reciprocates through an expansion stroke and an exhaust stroke during a single revolution of the crankshaft. A compression piston is received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke in a single rotation of the crankshaft. The compression cylinder is selectively controllable to place the compression piston in a compression mode or an idle mode. An air reservoir is operatively connected between the compression cylinder and the power cylinder and selectively operable to receive compressed air from the compression cylinder and to deliver compressed air to the power cylinder for use in transmitting power to the crankshaft during engine operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.12/006,988 filed Jan. 8, 2008, which is a continuation of U.S.application Ser. No. 11/326,909 filed Jan. 7, 2006, now U.S. Pat. No.7,353,786.

TECHNICAL FIELD

This invention relates to split-cycle engines and, more particularly, tosuch an engine incorporating an air hybrid system.

BACKGROUND OF THE INVENTION

The term split-cycle engine as used in the present application may nothave yet received a fixed meaning commonly known to those skilled in theengine art. Accordingly, for purposes of clarity, the followingdefinition is offered for the term split-cycle engine as may be appliedto engines disclosed in the prior art and as referred to in the presentapplication.

A split-cycle engine as referred to herein comprises:

a crankshaft rotatable about a crankshaft axis;

a power piston slidably received within a power cylinder and operativelyconnected to the crankshaft such that the power piston reciprocatesthrough a power (or expansion) stroke and an exhaust stroke during asingle rotation of the crankshaft;

a compression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression pistonreciprocates through an intake stroke and a compression stroke during asingle rotation of the crankshaft; and

a gas passage interconnecting the power and compression cylinders, thegas passage including an inlet valve and an outlet (or crossover) valvedefining a pressure chamber therebetween.

For purposes of clarity, the following is a list of acronyms for thevarious engine operating modes described herein:

AC Air compressor;

AM Air motoring;

CB Compression braking;

ICE Internal combustion engine;

PAP Pre-compressed air power;

PCA Pre-compressed combustion air.

United States patents U.S. Pat. No. 6,543,225 B2, U.S. Pat. No.6,609,371 B2 and U.S. Pat. No. 6,952,923, all assigned to the assigneeof the present invention, disclose examples of split-cycle internalcombustion engines as herein defined. These patents contain an extensivelist of United States and foreign patents and publications cited asbackground in the allowance of these patents. The term “split-cycle” hasbeen used for these engines because they literally split the fourstrokes of a conventional pressure/volume Otto cycle (i.e., intake,compression, power and exhaust) over two dedicated cylinders: onecylinder dedicated to the high pressure compression stroke, and theother cylinder dedicated to the high pressure power stroke.

Considerable research has been recently devoted to air hybrid engines ascompared, for example, to electric hybrid systems. The electric hybridsystem requires the addition to the conventional four stroke cycleengine of batteries and an electric generator and motor. The air hybridneeds only the addition of an air pressure reservoir added to an engineincorporating the functions of a compressor and an air motor, togetherwith the functions of a conventional engine, for providing the hybridsystem benefits. These functions include storing pressurized air duringbraking and using the pressurized air for driving the engine duringsubsequent starting and acceleration.

However, the prior art appears to involve only adapting a conventionalfour stroke cycle engine to perform the compression, combustion andmotoring functions in a single cylinder. This, then, requires a complexvalve and drivetrain system and control which is capable of switchingfrom a compression-braking (CB) mode to an air motoring (AM) mode andback to a conventional internal combustion engine (ICE) mode duringoperation.

In a typical example, when not storing or utilizing compressed air todrive the vehicle, a prior art air hybrid engine operates as aconventional internal combustion engine, where the four strokes of theOtto cycle (intake, compression, power and exhaust) are performed ineach piston every two revolutions of the crankshaft. However, during thecompression-braking mode, each cylinder of the conventional engine isconfigured to operate as a reciprocating piston two-stroke aircompressor, driven from the vehicle wheels by vehicle motion. Air isreceived from outside atmosphere into the engine cylinders, compressedthere, and displaced into an air-reservoir. Work performed by the enginepistons absorbs the kinetic energy of the vehicle and slows it down orrestricts its motion. In this way the kinetic energy of the vehiclemotion is transformed into energy of compressed air stored in the airreservoir.

During the air motoring mode, each cylinder of the engine is configuredto utilize the stored compressed air to produce power strokes forpropulsion without combustion. This may be accomplished by firstexpanding the stored, compressed air into the cylinders to drive thepistons down from top dead center (TDC) to bottom dead center (BDC) fora first power stroke. Then the pistons compress the expanded gas as theytravel from BDC to TDC. Fuel is then injected into the cylinders andignited just before TDC. The expanding products of combustion then drivethe pistons down again for a second power stroke on the secondrevolution of the crankshaft.

Alternatively, air-motoring may be accomplished by expanding the storedcompressed air to drive the power piston down from TDC to BDC for apower stroke without combustion for each revolution of the crankshaft.This alternative method of air motoring may continue until the pressurein the air reservoir falls below a threshold level, whereupon the enginemay switch to either the previously described air motoring mode or aconventional ICE engine mode of operation.

Problematically, in order to switch among the CB, AM and ICE modes, thevalve/drive train system becomes complex, costly and hard to control ormaintain. Additionally, since each cylinder must perform all of thefunctions for each mode, they cannot be optimized easily. For example,the pistons and cylinders must be designed to withstand an explosivecombustion event, even when just acting as an air compressor.Accordingly, due to the tolerances and materials required to withstandthe heat of combustion, some sacrifice must be made to the efficiency ofthe compressor mode.

Another problem with performing all functions for each mode (ICE, CB andAM) in every cylinder is that no two modes can be performed in parallel(i.e. simultaneously). Because prior art air hybrid systems utilizeconventional engines, they are restricted to operating in each modeserially, which imposes inherent limitations on their capabilities. Forexample, because the CB mode cannot be utilized when the engine isoperating as an internal combustion engine (in ICE mode), the airreservoir can only be charged during the braking function of a movingvehicle. This limitation leads to problems in maintaining the storedcharge in the air reservoir. Additionally, this limitation also meansthat prior art air hybrid systems are only applicable to movingvehicles, and are not practical for stationary applications such asstationary generators.

SUMMARY OF THE INVENTION

The present invention combines the features of the split cycle enginewith the air reservoir of the air hybrid concept and various simplifiedcontrol features to provide novel arrangements for operation and controlof the resulting hybrid engine embodiments. A distinct advantage of theinvention is that two or more engine modes as described herein can beoperated simultaneously (i.e., in parallel), because the split-cycleengine includes dedicated compression and power pistons.

Taken as a broad concept, a split-cycle air hybrid engine according tothe invention preferably includes:

a crankshaft rotatable about a crankshaft axis;

a power piston slidably received within a power cylinder and operativelyconnected to the crankshaft such that the power piston reciprocatesthrough an expansion (or power) stroke and an exhaust stroke during asingle rotation of the crankshaft;

a compression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression pistonreciprocates through an intake stroke and a compression stroke during asingle rotation of the crankshaft, the compression cylinder beingselectively controllable to place the compression piston in acompression mode or an idle mode;

an air reservoir operatively connected between the compression cylinderand the power cylinder and selectively operable to receive compressedair from the compression cylinder and to deliver compressed air to thepower cylinder for use in transmitting power to the crankshaft duringengine operation; and

valves selectively controlling gas flow into and out of the compressionand power cylinders and the air reservoir.

Alternatively, the power cylinder may also be selectively controllableto place the power piston in a power mode or an idle mode.

For purposes herein, when the compression piston is placed in idle mode,it means that for a single rotation of the crankshaft, the total amountof net negative work (opposing the direction of rotation of thecrankshaft) performed on the crankshaft by the compression piston isnegligible. Typically, negligible work in the compression piston's idlemode would be less than 20% of the negative work performed on thecrankshaft had the compression piston been in its compression mode.

Additionally for purposes herein, when the power piston is placed inidle mode, it means that for a single rotation of the crankshaft, thetotal amount of net positive work (advancing the direction of rotationof the crankshaft) performed on the crankshaft by the power piston isnegligible. Typically, negligible work in the power piston's idle modewould be less than 20% of the positive work performed on the crankshafthad the power piston been in its power mode.

In general, an engine according to the invention is capable of operationin at least three modes, including an internal combustion engine (ICE)mode, an air compressor (AC) mode and a pre-compressed air power (PAP)mode.

In the ICE mode, the compression piston and power piston are typicallyin their respective compressor and power modes. The compression pistondraws in and compresses inlet air for use in the power cylinder.Compressed air is admitted to the power cylinder with fuel shortly afterthe power piston reaches its top dead center (TDC) position at thebeginning of an expansion stroke. The fuel/air mixture is then ignited,burned and expanded on the same expansion stroke of the power piston,transmitting power to the crankshaft. The combustion products aredischarged on the exhaust stroke.

In the AC mode, the compression piston is in compression mode and drawsin and compresses air which is stored in the reservoir for later use inthe power cylinder.

In the PAP mode, the power cylinder is in power mode and receivescompressed air from the reservoir which is expanded on the expansionstroke of the power piston, transmitting power to the crankshaft. Theexpanded air is discharged on the exhaust stroke.

In certain preferred embodiments of the invention, power is developed inthe PAP mode in similar fashion to that of the ICE mode. That is, duringoperation in the PAP mode, fuel is mixed with the compressed air shortlyafter the power piston has reached its TDC position at the beginning ofan expansion stroke. The mixture is ignited, burned and expanded on thesame expansion stroke of the power piston, transmitting power to thecrankshaft. The combustion products are discharged on the exhauststroke.

In other alternative embodiments of the engine, power may be developedin the PAP mode in similar fashion to that of the previously describedair motoring modes. That is, during operation in the PAP mode, thecompressed air admitted to the power cylinder is expanded without addingfuel or initiating combustion.

In a first exemplary embodiment of the engine, the air reservoircomprises a gas passage sized to receive and store compressed air from aplurality of compression strokes, the gas passage interconnecting thecompression and power cylinders. The gas passage includes an inlet valveand an outlet valve defining a pressure chamber therebetween.

In a second exemplary embodiment of the engine, a gas passage alsointerconnects the compression and power cylinders, and the gas passageincludes an inlet valve and an outlet valve defining a pressure chambertherebetween. However, the air reservoir is connected by a reservoirpassage to the pressure chamber at a location between the inlet valveand the outlet valve.

A third exemplary embodiment of the engine adds a reservoir controlvalve in the reservoir passage to allow separation of the reservoir fromthe pressure chamber during ICE operation.

In a fourth exemplary embodiment of the engine, the air reservoir is anaccumulator adapted to maintain a relatively constant pressure thereinwithin a predetermined pressure range.

A fifth embodiment of the engine includes multiple pairs of compressionand power cylinders interconnected by gas passages having pressurechambers, wherein the pressure chambers are all connected with a singleair reservoir.

In a sixth alternative embodiment of the invention, the engine includesa gas passage interconnecting the compression and power cylinders, thegas passage including an inlet valve and an outlet valve defining apressure chamber therebetween. The air reservoir is connected inparallel with the gas passage, with inlet and outlet connections fromthe air reservoir to the compression and power cylinders.

These and other features and advantages of the invention will be morefully understood from the following detailed description of theinvention taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram showing a first embodiment of asplit-cycle air hybrid engine having an air reservoir and control valvesaccording to the invention;

FIG. 2 is a view similar to FIG. 1 but showing a second embodiment witha separate crossover (or gas) passage connected with the air reservoirand an added control valve;

FIG. 3 is a view similar to FIG. 2 but showing a third embodiment withan added reservoir control valve;

FIG. 4 is a view similar to FIG. 3 but showing a fourth embodimentincluding a constant pressure accumulator in the air reservoir;

FIG. 5 is a view similar to FIG. 3 showing a fifth embodiment having acommon reservoir for multiple cylinder pairs; and

FIG. 6 is a view similar to FIG. 3 showing a sixth embodiment having thereservoir in parallel with the crossover passage and separately valvedbetween the cylinders.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 1 of the drawings in detail, numeral 10generally indicates a first exemplary embodiment of a split cycle airhybrid engine according to the invention. Engine 10, shownschematically, is generally of the split-cycle type disclosed in theprior U.S. Pat. Nos. 6,543,225 B2, 6,069,371 B2 and 6,952,923 B2(Scuderi patents), herein incorporated by reference in their entirety.

As shown, the engine includes an engine block 12 having a first cylinder14 and an adjacent second cylinder 16 extending therethrough. Acrankshaft 18 is journaled in the block 12 for rotation about acrankshaft axis 20, extending perpendicular to the plane of the drawing.Upper ends of the cylinders 14, 16 are closed by a cylinder head 22

The first and second cylinders 14, 16 define internal bearing surfacesin which are received for reciprocation a first power piston 24 and asecond compression piston 26, respectively. The cylinder head 22, thepower piston 24 and the first cylinder 14 define a variable volumecombustion chamber 25 in the power cylinder 14. The cylinder head 22,the compression piston 26 and the second cylinder 16 define a variablevolume compression chamber 27 in the compression cylinder 16.

The crankshaft 18 includes axially displaced and angularly offset firstand second crank throws 28, 30, having a phase angle 31 therebetween.The first crank throw 28 is pivotally joined by a first connecting rod32 to the first power piston 24 and the second crank throw 30 ispivotally joined by a second connecting rod 34 to the second compressionpiston 26 to reciprocate the pistons in their cylinders in timedrelation determined by the angular offset of their crank throws and thegeometric relationships of the cylinders, crank and pistons.

Alternative mechanisms for relating the motion and timing of the pistonsmay be utilized if desired. The timing may be similar to, or varied asdesired from, the disclosures of the Scuderi patents. The rotationaldirection of the crankshaft and the relative motions of the pistons neartheir bottom dead center (BDC) positions are indicated by the arrowsassociated in the drawings with their corresponding components.

The cylinder head 22 includes any of various passages, ports and valvessuitable for accomplishing the desired purposes of the split-cycle airhybrid engine 10. In the illustrated first embodiment, the gaspassage/pressure chamber of the previously mentioned patents is replacedby a much larger air reservoir 36 connected to the head 22 through areservoir inlet port 38 opening into the closed end of the secondcylinder 16 and a reservoir outlet port 40 opening into the closed endof the first cylinder 14. As opposed to a smaller gas passage of a typeexemplified in the Scuderi patents, the air reservoir 36 is sized toreceive and store compressed air energy from a plurality of compressionstrokes of the compression piston 26. The second cylinder 16 alsoconnects with a conventional intake port 42 and the first cylinder 14also connects with a conventional exhaust port 44.

Valves in the cylinder head 22, which are similar to valves of theengine in the Scuderi patents, include a reservoir inlet check valve 46and three cam actuated poppet valves, a reservoir outlet valve (orcrossover valve) 50, a second cylinder intake valve 52, and a firstcylinder exhaust valve 54. The check valve 46 allows only one waycompressed air flow into the reservoir inlet port 38 from the second(compression) cylinder 16. The reservoir outlet valve 50 is opened toallow high pressure air flow from the reservoir 36 into the first(power) cylinder 14.

The present engine 10 includes two additional valves that may besolenoid actuated. These include an intake control valve 56 in thecylinder intake port 42 and a reservoir outlet control valve 58 in thereservoir outlet port 40. These valves may be two position on-off valvesbut could include variable position controls so that they could beoperated as throttle valves if desired.

The poppet valves 50, 52, 54 may be actuated by any suitable devices,such as camshafts 60, 62, 64 having cam lobes 66, 68, 70 respectivelyengaging the valves 50, 52, 54 for actuating the valves as will besubsequently discussed. Alternatively, the valves 50, 52 and 54, as wellas the other valves 46, 56 and 58, may be electronically, pneumaticallyor hydraulically actuated.

A spark plug 72 is also mounted in the cylinder head with electrodesextending into the combustion chamber 25 for igniting air-fuel chargesat precise times by an ignition control, not shown. It should beunderstood that the engine may be made as a diesel engine and beoperated without a spark plug if desired. Moreover, the engine 10 may bedesigned to operate on any fuel suitable for reciprocating pistonengines in general, such as hydrogen or natural gas.

FIGS. 2 through 6 of the drawings disclose various alternativeembodiments which are variations of the engine 10 of FIG. 1 and aredescribed below. Operation of all six of the exemplary embodiments willbe described thereafter.

Referring to FIG. 2, s second embodiment of engine 74 is disclosedwherein like reference numerals indicate like parts. Engine 74 isgenerally similar to engine 10, but differs in that a small volumecrossover (or gas) passage 76 is connected between the inlet port 38 andinlet check valve 46 at one end and the outlet port 40 and outlet valve50 at an opposite end. This crossover passage 76 extends between thecompression chamber 27 in the second cylinder 16 and the combustionchamber 25 in the first cylinder 14 and is similar to the crossoverpassage in the prior Scuderi patents. As opposed to an air reservoir,this crossover passage 76 is not sized to store a substantial amount ofcompressed air energy for later use. Rather the passage 76 is typicallydesigned to be as small as practically possible for the most efficienttransfer of compressed gas during the ICE mode of the engine 74.

In an additional modification, separate air reservoir 36 is connectedthrough a reservoir runner or reservoir passage 78 to the crossoverpassage 76 and connects to the inlet and outlet ports 38, 40 through thecrossover passage 76. The reservoir outlet solenoid control valve 58 islocated in the passage 76 between the outlet port 40 and the reservoirrunner 78. Valve 58 is open during ICE mode to allow compressed air tofollow the path of least resistance and flow primarily through passage76 into combustion chamber 25. Valve 58 may be closed during AC mode topump compressed air into reservoir 36 and may be open during PAP mode toretrieve compressed air from the reservoir 36.

Referring now to FIG. 3 of the drawings, a third embodiment of engine 80is disclosed, which differs from engine 74 in FIG. 3, only in theaddition of a third solenoid valve 82. Valve 82 is located in the runner78 at its junction with the crossover passage 76 to cut off theconnection of the air reservoir 36 with the crossover passage whendesired.

By isolating the air reservoir 36 via valve 82, the overall engine 80performance can be more effectively optimized during the ICE mode ofoperation. For example, during the ICE mode all compressed air can bemade to flow through the crossover passage 76. Accordingly, thecrossover passage 76 can be designed for the most efficient transfer ofgas without interacting with the air reservoir. Additionally valve 82can also be utilized as a throttling valve for part load conditionsduring the PAP mode.

FIG. 4 shows a fourth embodiment of engine 84 similar to the engine 80of FIG. 3. It differs in the conversion of the air reservoir into apressure accumulator 86 by the addition of a diaphragm or bladder 87 andspring mechanism 88. These act to pressurize air that is present in theaccumulator 86 and to maintain the contents at a relatively constantpressure between conditions where the reservoir is either empty or isfilled up to the maximum control pressure.

FIG. 5 illustrates a fifth embodiment of a multicylinder engine 89having at least two cylinder pairs 90, each equivalent to the engine 80of FIG. 3. Engine 89 is modified to include a common supply reservoir 92that is joined to crossover passages 76 of all the cylinder pairs with areservoir control solenoid valve 82 controlling communication of eachreservoir runner 78 with its respective crossover passage 76.

FIG. 6 discloses a sixth embodiment of engine 94 that is most similar toengine 80 of FIG. 3. Engine 94 differs in that the air reservoir 36 isseparated from direct connection with the crossover passage 76, whichremains controlled by check valve 46, solenoid valve 58 and outlet valve50. The air reservoir 36 is connected in parallel with the crossoverpassage 76 by first and second reservoir runners (or passages) 96, 98,respectively connecting the reservoir directly to the combustion chamber25 of the first cylinder 14 and the compression chamber 27 of the secondcylinder 16. Fourth and fifth solenoid control valves 100, 102respectively control flow between the runners 96, 98 and the cylinders14, 16.

Operation of the described exemplary embodiments of split-cycle airhybrid engines according to the invention will now be discussed forpurposes of explanation and not of limitation, it being understood thatadditional methods and variations will be apparent that should properlyfall within the intended scope of the invention.

Basically, split-cycle air hybrid engines of the present invention aretypically operable in at least three modes, an internal combustionengine (ICE) mode, an air compressor (AC) mode and a pre-compressed airpower (PAP) mode. The PAP mode preferably includes a pre-compressedcombustion-air power (PCA) mode wherein pre-compressed air and fuel aremixed shortly after the power piston reaches its top dead centerposition during an expansion stroke and then the fuel/air mixture iscombusted to drive the power piston down during the same expansionstroke. Alternatively, the PAP mode could also include various forms ofair motoring (AM) modes (as previously exemplified herein) whereinpre-compressed air is utilized to provide an expansion stroke withoutcombustion. As will be discussed in greater detail, because thesplit-cycle air hybrid of the present invention has separate dedicatedcompression and power cylinders, the three modes, ICE, AC and PAP, canbe run either serially or in parallel as desired.

The ICE mode is basically the normal operating mode of the enginesdisclosed in the previously mentioned Scuderi patents. The intake,compression, power and exhaust strokes of a conventional piston enginecycle are split between the compression and power cylinders of thesplit-cycle engine.

Referring to the embodiment of FIG. 1, split cycle engines as describedin the Scuderi U.S. Pat. Nos. (6,543,225, 6,609,371 and 6,952,923)include structural parameters that are advantageous over prior artsplit-cycle engines. Many of these advantages will be described inrelation to the following discussion of the ICE mode of the engine 10.It is important to note that the air reservoir 36 of FIG. 1 performs thecombined functions of both the separated crossover (or gas) passage 76and air reservoir 36 of subsequent FIGS. 2-6.

In the ICE mode, the intake solenoid valves 56, 58 remain open. On theintake stroke, intake valve 52 opens as the compression piston movesdown, drawing in air to the compression chamber 27. On the compressionstroke, the intake valve 52 closes and the piston 26 moves up,compressing the air and forcing it through the check valve 46 and theinlet port 38 into the air reservoir 36.

The power piston 24 leads the compression piston 26 by a phase angle 31that is substantially greater than 0 degrees of rotation of thecrankshaft. The phase angle 31 as defined herein is the degrees of crankangle (CA) rotation the crankshaft 18 must rotate after the power piston24 has reached its top dead center (TDC) position in order for thecompression piston 26 to reach its respective TDC position. In theparticular embodiment illustrated in FIG. 1, the magnitude of the anglebetween the first and second crank throws 28 and 30 is equal to thephase angle 31. Preferably this phase angle is between 10 and 40 degreesCA and more preferably between 20 and 30 degrees CA. The phase angle 31is sized such that as the compression piston 26 ascends toward its TDCposition and the power piston descends from its TDC position, asubstantially equal mass of compressed air is transferred into and outof the air reservoir 36 (in subsequent FIGS. 2-6 a substantially equalmass of compressed air is transferred into and out of the gas passage76).

On the power stroke, outlet (or crossover) valve 50 is typically open atTDC of the power piston 24. Preferably the outlet valve 50 is openedwithin a range of 10 to 0 degrees CA before TDC of the power piston 24,and more preferably within a range of 7 to 3 degrees CA before TDC ofthe power piston. The outlet valve 50 is preferably closed within arange of 10 to 40 degrees CA after TDC of the power piston 24, and morepreferably closes within a range of 20 to 30 degrees CA after TDC of thepower piston.

The power piston 24 descends from its TDC position toward a combustionignition position, which is typically within a range of 5 to 40 degreesCA after TDC and more preferably within a range of 10 to 30 degrees CAafter TDC. Fuel may be injected and mixed with the compressed air by atleast two methods, i.e., either in the air reservoir 36 just up streamof the outlet valve 50 (port fuel injection), or directly into the powercylinder 14 (direct injection). Once the power piston 24 reaches itscombustion ignition position, the fuel/air mixture is ignited by sparkplug 72 (or compression ignition if a diesel engine), forcing the piston24 down to BDC and delivering power to the crankshaft 18. The pressureat which combustion ignition occurs is the ignition (or firing)condition pressure.

On the exhaust stroke, the exhaust valve 54 opens and crossover valve 50is closed. As the power piston 24 moves upward from BDC to TDC, thespent exhaust gases are forced out of the combustion chamber 25 throughthe exhaust port 44.

The intake and compression strokes for a pressure/volume cycle withinthe engine take place during the same crankshaft revolution as the powerand exhaust strokes of the cycle, except that the power and exhauststrokes are advanced by the fixed phase angle 31. Thus a newpressure/volume cycle is completed each revolution of the enginecrankshaft instead of in two revolutions as in a conventionalfour-stroke engine. However, the inlet valve 46 and outlet valve 50maintain the gas pressure within the air reservoir 36 at or aboveignition (or firing) condition pressure during the entire four-strokecycle.

One of the basic differences between the Scuderi Split-Cycle and theprior art is the parameter that pressure in the gas passage ismaintained at or above the firing condition pressure during all fourstrokes of the Otto cycle combined with the parameter that ignition inthe power cylinder occurs substantially after top dead center (i.e.,more than 5 degrees and preferably more than 10 degrees ATDC). This setsup a condition where the combustion event (or flame speed) is very fast(occurring within 24 degrees CA or less), and the NOx emissions outputis very low (50 to 80 percent less than a conventional engine). Anotherunique aspect of the Scuderi Split-Cycle, not found in the prior art, isthat the centerline of the power and compression cylinders are offsetfrom the crankshaft axis. This enables the piston skirt to cylinder wallfriction to be substantially reduced. All three of these advantageousfeatures (maintaining firing condition pressures in the gas passage,firing after top dead center, and the offsets) are disclosed and claimedin the Scuderi Patents.

In addition to the above parameters, several other parameters have alsobeen identified in the Scuderi Patents, which have a significant effecton engine efficiency. These parameters include:

1. Maintaining the compression and expansion ratios equal to or greaterthan 26 to 1, preferably equal to or greater than 40 to 1, and morepreferably equal to or greater than 80 to 1;

2. The crossover valve duration (amount of crank angle (CA) rotationneeded to open and close valve 50) should be equal to or less than 69degrees, preferably less than 50 degrees, and more preferable less than35 degrees; and

3. The crossover valve 50 should be open for a small percentage of timeafter combustion is initiated in the power cylinder.

During braking of a vehicle driven by an engine 10, the engine isswitched to operation in the air compressor (AC) mode. Fuel injection isstopped and the solenoid valve 58 is closed, preventing air flow throughthe outlet port 40 and suspending power delivery from the power piston24, thus placing the power piston 24 in an idle mode. However, thecompression piston continues to operate, driven by the inertia of themoving vehicle, and to pump the compressed air into the air reservoir36. The pumping action effectively slows, or brakes, the vehicle and thebraking action becomes increasingly effective as the reservoir airpressure increases. The increased pressure in the reservoir is retainedfor later use in the PAP mode.

While in AC mode, the exhaust valve 54 may be held open to reduce idlinglosses on the power piston 24. Moreover, the power piston could be usedto increase the braking effect in various ways, such as by altering thevalve timing and operation to draw in and compress further air into theair reservoir. Alternatively (to keep the air reservoir clean), thepiston 24 could be used as a conventional compression brake, drawing inair on the downstroke, compressing it on the upstroke and opening theexhaust valve 54 near top dead center (TDC) to discharge the compressedair and dissipate its energy. This could increase braking and reducebrake wear but would limit the recovery of energy from the compressedair in the PCA or AM modes.

Referring still to FIG. 1, the preferred third mode of operation ispre-compressed combustion air (PCA) which, from prior AC operation, hasstored compressed air in the reservoir 36 at a higher pressure thangenerally occurs in ICE operation. The engine has at least slowed downand is ready to be accelerated. To run the PCA mode, the outlet solenoidvalve 58 is opened and spark ignition and fuel injection functions arereactivated. Also, the compression piston is idled by holding open boththe intake valve 52 and the intake solenoid valve 56 so that thecompression piston 26 moves freely without resistance and no air iscompressed or added to the reservoir 36.

If valve 52 is not independently adjustable, the compression piston 26may also be placed in idle mode by closing solenoid valve 56. In thisway the compression piston alternately compresses and expands the gastrapped in the cylinder. The compression and expansion of the trappedgas alternates the negative and positive work done on the crankshaft bythe piston. Since the negative and positive work is approximately equal,the net work done on the crankshaft by the piston operating in this modeis negligible. Still another method of placing the compression piston inidle mode is to prevent the compression piston 26 from reciprocating byoperatively disconnecting it from the crankshaft 18. In any of the aboveexamples of the compression piston's idle mode, the total amount of netnegative work done on the crankshaft is negligible.

Shortly after or just prior to TDC of the power piston 24, as in ICEoperation, the reservoir outlet valve 50 opens, forcing a charge ofcompressed air (preferably controlled and with added fuel) from thereservoir 36 into the combustion chamber. Within a range of 5 to 40degrees CA after TDC, and preferably within a range of 10 to 20 degreesCA after TDC, the fuel is quickly ignited and burns on the power stroke,providing power to the crankshaft. Exhaust products are discharged onthe exhaust upstroke and the cycle is repeated.

As the vehicle is accelerated and returns to normal operation, thestored high pressure air continues to be used for combustion in thepower cylinder 14 until the pressure drops to a normal operatingpressure and the engine is returned to full ICE operation. However,operation in PCA mode as long as possible increases operating efficiencybecause compression energy from braking is returned to the PCA powercycle while the compressor piston 26 is idling using very little energy.Thus the vehicle braking compression energy is used to providecompression energy in the PCA power mode.

If the engine is stopped, stored compression energy can be used to startthe engine, and the vehicle if desired, until a minimum speed isreached, whereupon the engine may be returned to ICE operation. However,a backup electric starter may be desirable.

Referring again to FIG. 2, operation of the engine 72 is similar to thatof engine 10 (FIG. 1). However, use of the small volume crossoverpassage 76 for flow between cylinders substantially avoids flow throughthe air reservoir 36 during ICE operation and potentially reducesundesirable pressure variations in the gas passage 76 that couldadversely affect engine performance.

In the embodiment of FIG. 3, the addition of the solenoid valve 82 atthe reservoir connection with the crossover passage 76 allows cuttingoff the reservoir to maintain a higher or lower pressure therein whilethe smaller crossover passage 76 can operate with rapidly changingpressures in normal ICE engine operation for a split cycle engine.

In FIG. 4, the replacement of the air reservoir with an accumulator 86allows the storage of a range of air volumes at a relatively constantpressure for use, primarily, in controlling air charge volumes deliveredto the combustion chamber by controlling only the outlet valve 50opening time.

The use of a common air reservoir, or accumulator, as in FIG. 5, mayreduce manufacturing costs. Although the common air reservoir isillustrated in FIG. 5 as connected directly to the gas passages, oneskilled in the art would recognize that the air reservoir may beconfigured to connect to the split-cycle engine in other ways. Forexample, the common air reservoir may be an integral part of the gaspassage as in FIG. 1, or may be connected in parallel with the gaspassage as in FIG. 6.

The embodiment of FIG, 6 further separates the effects of the airreservoir 36 on pressures in the crossover passage 76 and allows morecomplete separation of operation in the ICE mode from either the AC modeor the PCA mode.

Referring to FIGS. 1-6 in general, a distinct advantage of the presentinvention is that air hybrid systems utilizing a split-cycle engine 10,74, 80, 84, 89 and 94 can function in the various operating modes (ICE,AC and PAP) simultaneously (or in parallel) over the paired compressioncylinders 16 and power cylinders 14, rather than being restricted tooperating each mode serially out of a single cylinder. This parallelmode ability inherently provides added capabilities and expandedapplications for split-cycle air hybrid systems.

Referring now to FIG. 3 as an example, under part load conditions theengine 80 can simultaneously operate in the ICE mode while continuouslycharging the air reservoir in the AC mode. That is, a full charge of airmay be made to enter the compression cylinder 16 on an intake strokewhere it is compressed and forced into gas passage 76. However, only afraction of the air charge is required to operate the ICE mode underpart load conditions. Accordingly, only a portion of the charge may berouted to the power cylinder 14 while the remainder of the charge can bediverted to the air reservoir 36 to keep it fully charged. In this way,split-cycle air hybrid systems have the ability to continuously chargetheir air reservoirs under part load conditions.

Additionally, in much the same fashion, waste energy from exhaust gascan be re-circulated, either directly or through a turbocharger, backinto the intake of a split-cycle air hybrid engine 80 to be stored ascompressed air energy in the air reservoir 36. Advantageously, thistechnique of recovering exhaust gas energy while operating under partload conditions can also be utilized in stationary applications, e.g.,in stationary generators.

Although the invention has been described by reference to certainspecific embodiments, it should be understood that numerous changes maybe made within the spirit and scope of the inventive concepts disclosed.Accordingly, it is intended that the invention not be limited to thedescribed embodiments, but that it have the full scope defined by thelanguage of the following claims.

1-9. (canceled)
 10. An engine comprising: a crankshaft rotatable about acrankshaft axis; a power piston slidably received within a powercylinder and operatively connected to the crankshaft such that the powerpiston reciprocates through an expansion stroke and an exhaust strokeduring a single rotation of the crankshaft and such that the ratio ofthe volume in the power cylinder when the power piston is at its bottomdead center (BDC) position to the volume in the power cylinder when thepower piston is at its top dead center (TDC) position is 26 to 1 orgreater; a compression piston slidably received within a compressioncylinder and operatively connected to the crankshaft such that thecompression piston reciprocates through an intake stroke and acompression stroke during a single rotation of the crankshaft; a gaspassage interconnecting the compression and power cylinders, the gaspassage including an inlet valve and an outlet valve defining a pressurechamber therebetween; and an air reservoir connected by a reservoirpassage to the pressure chamber at a location between the inlet valveand the outlet valve, the reservoir passage being selectively operableto receive compressed air from the compression cylinder to the airreservoir, and to deliver compressed air from the air reservoir to thepower cylinder; wherein the engine is operable in a pre-compressed airpower (PAP) mode, wherein in the PAP mode: the power cylinder receives afirst charge of compressed air from the air reservoir during a firstexpansion stroke of the power piston; said first charge of compressedair is mixed with fuel during said first expansion stroke; andcombustion of the fuel is initiated in the power cylinder during saidfirst expansion stroke.
 11. The engine of claim 10, wherein the ratio ofthe volume in the power cylinder when the power piston is at its bottomdead center (BDC) position to the volume in the power cylinder when thepower piston is at its top dead center (TDC) position is 40 to 1 orgreater.
 12. The engine of claim 10, wherein during the PAP mode,combustion of the fuel is initiated between 5 to 40 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 13. Theengine of claim 10, wherein during the PAP mode, combustion of the fuelis initiated between 5 to 30 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 14. The engine of claim 10, whereinduring the PAP mode, combustion of the fuel is initiated between 10 to30 degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 15. The engine of claim 11, wherein during the PAP mode,combustion of the fuel is initiated between 5 to 40 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 16. Theengine of claim 11, wherein during the PAP mode, combustion of the fuelis initiated between 5 to 30 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 17. The engine of claim 11, whereinduring the PAP mode, combustion of the fuel is initiated between 10 to30 degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 18. The engine of claim 10, wherein the outlet valve is openafter combustion is initiated in the power cylinder and during saidfirst expansion stroke.
 19. The engine of claim 10, wherein the numberdegrees of angle of the crankshaft required to open and close the outletvalve is 69 degrees or less during the PAP mode.
 20. The engine of claim10, wherein the number degrees of angle of the crankshaft required toopen and close the outlet valve is 50 degrees or less during the PAPmode.
 21. The engine of claim 10, wherein the number degrees of angle ofthe crankshaft required to open and close the outlet valve is 35 degreesor less during the PAP mode.
 22. The engine of claim 10, wherein theratio of the volume in the power cylinder when the power piston is atits bottom dead center (BDC) position to the volume in the powercylinder when the power piston is at its top dead center (TDC) positionis 26 to 1 or greater at full load.
 23. The engine of claim 10, whereinthe ratio of the volume in the power cylinder when the power piston isat its bottom dead center (BDC) position to the volume in the powercylinder when the power piston is at its top dead center (TDC) positionis 40 to 1 or greater at full load.
 24. The engine of claim 10, whereinthe outlet valve is open after combustion is initiated in the powercylinder and during said first expansion stroke at full load.
 25. Theengine of claim 10, wherein the engine is operable in an air compressor(AC) mode such that the compression piston operates in a compressionmode, in the compression mode the compression piston draws in andcompresses air which is stored in the air reservoir via the reservoirpassage for later use in the power cylinder.
 26. The engine of claim 25,wherein the compression piston operates in an idle mode while the engineis in the PAP mode, wherein, in the idle mode, the total amount of workopposing the direction of rotation of the crankshaft (net negative work)is less than 20 percent of the net negative work performed on thecrankshaft had the compression piston been in its compression mode. 27.The engine of claim 26, comprising an intake valve disposed in thecompression cylinder, wherein, the intake valve is held open when thecompression piston operates in the idle mode.
 28. The engine of claim10, wherein the air reservoir is an accumulator allowing storage of arange of air volumes.
 29. The engine of claim 10, wherein the airreservoir is an accumulator allowing storage of a range of air volumesat a relatively constant pressure.
 30. An engine comprising: acrankshaft rotatable about a crankshaft axis; a power piston slidablyreceived within a power cylinder and operatively connected to thecrankshaft such that the power piston is operable to reciprocate throughan expansion stroke and an exhaust stroke during a single rotation ofthe crankshaft and such that the ratio of the volume in the powercylinder when the power piston is at its bottom dead center (BDC)position to the volume in the power cylinder when the power piston is atits top dead center (TDC) position is 26 to 1 or greater; an airreservoir selectively operable to receive compressed air and to delivercompressed air to the power cylinder; a crossover passageinterconnecting the air reservoir and the power cylinder and includingan air reservoir valve operable to control air flow between the airreservoir and the crossover passage and an outlet valve operable tocontrol air flow between the crossover passage and the power cylinder;wherein the engine is configured to operate in a pre-compressed airpower (PAP) mode, wherein in the PAP mode: the power cylinder receives afirst charge of compressed air from the air reservoir through thecrossover passage during a first expansion stroke of the power piston;said first charge of compressed air is mixed with fuel during said firstexpansion stroke; and combustion of the fuel is initiated in the powercylinder during said first expansion stroke.
 31. The engine of claim 30,wherein the ratio of the volume in the power cylinder when the powerpiston is at its bottom dead center (BDC) position to the volume in thepower cylinder when the power piston is at its top dead center (TDC)position is 40 to 1 or greater.
 32. The engine of claim 30, whereinduring the PAP mode, combustion of the fuel is initiated between 5 to 40degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 33. The engine of claim 30, wherein during the PAP mode,combustion of the fuel is initiated between 5 to 30 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 34. Theengine of claim 30, wherein during the PAP mode, combustion of the fuelis initiated between 10 to 30 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 35. The engine of claim 31, whereinduring the PAP mode, combustion of the fuel is initiated between 5 to 40degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 36. The engine of claim 31, wherein during the PAP mode,combustion of the fuel is initiated between 5 to 30 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 37. Theengine of claim 31, wherein during the PAP mode, combustion of the fuelis initiated between 10 to 30 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 38. The engine of claim 30, whereinthe outlet valve is proximate the power cylinder.
 39. The engine ofclaim 38, wherein the outlet valve is open after combustion is initiatedin the power cylinder and during said first expansion stroke.
 40. Theengine of claim 38, wherein the number degrees of angle of thecrankshaft required to open and close the outlet valve is 69 degrees orless during the PAP mode.
 41. The engine of claim 38, wherein the numberdegrees of angle of the crankshaft required to open and close the outletvalve is 50 degrees or less during the PAP mode.
 42. The engine of claim38, wherein the number degrees of angle of the crankshaft required toopen and close the outlet valve is 35 degrees or less during the PAPmode.
 43. The engine of claim 30, wherein the ratio of the volume in thepower cylinder when the power piston is at its bottom dead center (BDC)position to the volume in the power cylinder when the power piston is atits top dead center (TDC) position is 26 to 1 or greater at full load.44. The engine of claim 30, wherein the ratio of the volume in the powercylinder when the power piston is at its bottom dead center (BDC)position to the volume in the power cylinder when the power piston is atits top dead center (TDC) position is 40 to 1 or greater at full load.45. The engine of claim 38, wherein the outlet valve is open aftercombustion is initiated in the power cylinder and during said firstexpansion stroke at full load.
 46. The engine of claim 30, wherein theengine is operable in an air compressor (AC) mode such that acompression piston operates in a compression mode, wherein in thecompression mode the compression piston draws in and compresses airwhich is stored in the air reservoir via a reservoir passage for lateruse in the power cylinder.
 47. The engine of claim 46, wherein thecompression piston operates in an idle mode while the engine is in thePAP mode, wherein, in the idle mode, the total amount of work opposingthe direction of rotation of the crankshaft (net negative work) is lessthan 20 percent of the net negative work performed on the crankshaft hadthe compression piston been in its compression mode.
 48. The engine ofclaim 47, comprising an intake valve disposed in the compressioncylinder, wherein, the intake valve is held open when the compressionpiston operates in the idle mode.
 49. The engine of claim 30, whereinthe air reservoir is an accumulator allowing storage of a range of airvolumes.
 50. The engine of claim 30, wherein the air reservoir is anaccumulator allowing storage of a range of air volumes at a relativelyconstant pressure.
 51. The engine of claim 30, further comprising: acompression piston slidably received within a compression cylinder andoperatively connected to the crankshaft such that the compression pistonreciprocates through an intake stroke and a compression stroke during asingle rotation of the crankshaft; and wherein the crossover passageinterconnects the compression and power cylinders and includes an inletvalve and said outlet valve defining a pressure chamber therebetween andwherein the air reservoir valve is operable to control air flow betweenthe air reservoir and the pressure chamber.
 52. An engine comprising: acrankshaft rotatable about a crankshaft axis; a power piston slidablyreceived within a power cylinder and operatively connected to thecrankshaft such that the power piston is operable to reciprocate throughan expansion stroke and an exhaust stroke during a single rotation ofthe crankshaft; an air reservoir selectively operable to receivecompressed air and to deliver compressed air to the power cylinder,wherein the air reservoir is an accumulator allowing storage of a rangeof air volumes; at least one valve operable to selectively control airor gas flow between the air reservoir and the power cylinder; whereinthe engine is configured to operate in a pre-compressed air power (PAP)mode, wherein in the PAP mode: the power cylinder receives a firstcharge of compressed air from the air reservoir during a first expansionstroke of the power piston; said first charge of compressed air is mixedwith fuel during said first expansion stroke; and combustion of the fuelis initiated in the power cylinder during said first expansion stroke.53. The engine of claim 52, wherein the air reservoir is an accumulatorallowing storage of a range of air volumes at a relatively constantpressure.
 54. The engine of claim 52, wherein the ratio of the volume inthe power cylinder when the power piston is at its bottom dead center(BDC) position to the volume in the power cylinder when the power pistonis at its top dead center (TDC) position is 26 to 1 or greater.
 55. Theengine of claim 52, wherein the ratio of the volume in the powercylinder when the power piston is at its bottom dead center (BDC)position to the volume in the power cylinder when the power piston is atits top dead center (TDC) position is 40 to 1 or greater.
 56. The engineof claim 52, wherein during the PAP mode, combustion of the fuel isinitiated between 5 to 40 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 57. The engine of claim 52, whereinduring the PAP mode, combustion of the fuel is initiated between 5 to 30degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 58. The engine of claim 52, wherein during the PAP mode,combustion of the fuel is initiated between 10 to 30 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 59. Theengine of claim 54, wherein during the PAP mode, combustion of the fuelis initiated between 5 to 40 degrees of crank angle (CA) after top deadcenter (TDC) of the power piston.
 60. The engine of claim 54, whereinduring the PAP mode, combustion of the fuel is initiated between 5 to 30degrees of crank angle (CA) after top dead center (TDC) of the powerpiston.
 61. The engine of claim 54, wherein during the PAP mode,combustion of the fuel is initiated between 10 to 30 degrees of crankangle (CA) after top dead center (TDC) of the power piston.
 62. Theengine of claim 52, wherein the at least one valve is an outlet valveproximate the power cylinder.
 63. The engine of claim 62, wherein theoutlet valve is open after combustion is initiated in the power cylinderand during said first expansion stroke.
 64. The engine of claim 62,wherein the number degrees of angle of the crankshaft required to openand close the outlet valve is 69 degrees or less during the PAP mode.65. The engine of claim 62, wherein the number degrees of angle of thecrankshaft required to open and close the outlet valve is 50 degrees orless during the PAP mode.
 66. The engine of claim 62, wherein the numberdegrees of angle of the crankshaft required to open and close the outletvalve is 35 degrees or less during the PAP mode.
 67. The engine of claim52, wherein the ratio of the volume in the power cylinder when the powerpiston is at its bottom dead center (BDC) position to the volume in thepower cylinder when the power piston is at its top dead center (TDC)position is 26 to 1 or greater at full load.
 68. The engine of claim 52,wherein the ratio of the volume in the power cylinder when the powerpiston is at its bottom dead center (BDC) position to the volume in thepower cylinder when the power piston is at its top dead center (TDC)position is 40 to 1 or greater at full load.
 69. The engine of claim 62,wherein the outlet valve is open after combustion is initiated in thepower cylinder and during said first expansion stroke at full load. 70.The engine of claim 52, wherein the engine is operable in an aircompressor (AC) mode such that a compression piston operates in acompression mode, wherein in the compression mode the compression pistondraws in and compresses air which is stored in the air reservoir via areservoir passage for later use in the power cylinder.
 71. The engine ofclaim 70, wherein the compression piston operates in an idle mode whilethe engine is in the PAP mode, wherein, in the idle mode, the totalamount of work opposing the direction of rotation of the crankshaft (netnegative work) is less than 20 percent of the net negative workperformed on the crankshaft had the compression piston been in itscompression mode.
 72. The engine of claim 71, comprising an intake valvedisposed in the compression cylinder, wherein, the intake valve is heldopen when the compression piston operates in the idle mode.
 73. Theengine of claim 62, further comprising: a compression piston slidablyreceived within a compression cylinder and operatively connected to thecrankshaft such that the compression piston reciprocates through anintake stroke and a compression stroke during a single rotation of thecrankshaft; and a gas passage interconnecting the compression and powercylinders, the gas passage including an inlet valve and said outletvalve defining a pressure chamber therebetween.